In my experience organizations are either "voice driven" (voice mail or phone calls move the organization along) or "email driven". Generally speaking, the more international an organization is, the more email driven it becomes just so it can deal with the timezone differences.
I've found that once you are in an email driven organization, there is something of a competitive advantage to reading and writing email at odd hours, weekends and holidays. For example, just because it is Memorial Day in the U.S. doesn't mean it's a holiday in Japan. So if you respond to emails while others in your organization are out camping, you get to drive the agenda. By the time your organizational competition has put their Coleman laterns away, you've set the terms and conditions and have a lock on the deal.
So does this mean you sit by your computer while everyone else is having fun? Not really. I spent time in the surf this past Sunday, but still did a good dozen emails with Asia and the Middle East. The thing about keeping an email dialog going is that it really doesn't take a lot of time. After rinsing out my wetsuit I glanced at my computer to see what emails came in while I was getting my butt kicked by some big waves. I shot out some responses before eating lunch, took less than 15 minutes. Sent some follow-ups that Sunday evening. By the time others started reading their emails Monday morning I had already taken care of the situation.
Of course it helps that I have hobbies that don't take me away from civilization for long stretches of time. I hate camping.